A study will be made to determine the bactericidal capabilities of purified lactoferrin (LF) and of LF in saliva of immunodeficient and normal subjects. Potential mechanisms of biological action will be investigated by comparing the metabolic characteristics of lactoferrin resistant and sensitive microbial strains. Levels of unsaturated lactoferrin will be determined in saliva samples and correlated with possible functional biological activity. Interactions of lactoferrin with other salivary proteins and their possible synergistic effects on the bactericidal function of lactoferrin will be investigated. Levels of lactoferrin, its location and nature in dental plaque will be studied by extraction, immunochemical and immunohistochemical methods.